Metallizing of plastic materials

ABSTRACT

IN METALLIZING OF PLASTICS, THE PLASTIC ARTICLES ARE SENSITIZED WITH AN ACID SOLUTION OF A TRIVALENT METAL OF THE 5TH MAIN GROUP OF THE PERIODIC TABLE, E.G. ARSENIC, AND ARE THEREAFTER SUBJECTED TO AN ELECTROLYTIC METALLIZING STEP.

Unitecl States Patent Ofice 3,764,488 Patented Oct. 9, 1973 3,764,488 METALLIZING OF PLASTIC MATERIALS Gunther Bernhardt, Haugelar, Germany, assignor to Dynamit Nobel AG, Troisdorf, Germany No Drawing. Filed Aug. 28, 1970, Ser. No. 68,018

Claims priority, application Germany, Sept. 1, 1969, P 19 44 314.2

Int. Cl. B44d 1/092; C23b /62; C23f 17/00 US. Cl. 204-38 B 12 Claims ABSTRACT OF THE DISCLOSURE In metallizing of plastics, the plastic articles are sensitized with an acid solution of a trivalent metal of the 5th main group of the Periodic Table, e.g. 31801110, and are thereafter subjected to an electrolytic metallizing step.

BACKGROUND It is known to provide plastic materials with firmly adherent metal coatings by applying chemically to pretreated plastic surfaces, a thin metallic conductor layer of copper or nickel, copper, chromium, silver, gold, or, if desired by several of these metals (cf. K. Wiebusch et al., Plastics 56, (1966) 773). It is further known the ABS plastics (graft-type copolymers made of acrylonitnle, butadiene and styrene known in the art to be suitable for the subject treatment) can be metallized by application of the so called travel-through process (cf. K. Heymann et al., Galvanotechnik 59 (1968) 652-658, W. Metzger et al., Galvanotechnik 58 (1967) 720-722) without coating with metal the insulation of the electrodes serving simultaneously as an electrode member and as a support for the ABS part being metallized. As a result, on the one hand, one obviates the need for another plugging-in of the parts following the chemical metallization and, on the other, one achieves a metal savings in v1ew of the fact that the metal is being deposited only onto the plastic to be metallized.

Accordingly, the travel-through principle is a chemogalvanic or chemo-electrolytic metallizing process in which the parts to be metallized remain plugged onto the same supporting element during both the chemical metalllzmg processes and the galvanic reinforcing processes so that all process phases can be performed in sequence without any interruption to re-mount the parts to be metallized.

The travel-through process hitherto known comprises the following steps:

(1) Pickling of the ABS parts in an acid solution, e.g. chromosulphuric acid of predominantly high chromic acid content (up to 300 g. CrO /l.) at 50-70" C.

(2) Activation in highly acid noble metal salt solution,

e.g. palladium salt solution at 55-65" C.

(3) Immersion of the activated parts in a reducing solution subject to maintaining certain pH conditions.

(4) Chemical depositing of a metallic conductor layer consisting for instance of nickel and/or copper.

(5) Galvanic reinforcement by means of nickel, copper, chromium, silver, gold, or if desired by several of these metals.

However, the methods that have hitherto become known in the art for travel-through processes have disadvantages. For instance, their application is limited to ABS plastics only. Metallizing of per se metallizable polyvinyl chloride types or metallizable polypropylene types according to the known travel-through processes is not possible.

Moreover, the composition of the activating bath (2) makes it necessary, in order to achieve an optimum activation of immersed parts, working at increased bath temperature, namely within a narrow temperature range of 55-65 C. Further, frequently a loss of noble metal,

e.g. palladium, occurs as a result of depositing of the noble metal on equipment, requiring a constant upkeep of the activation bath.

THE INVENTION Now the object of the invention is a process for the chemo-galvanic or electrolytic metallization of plastics with adherent metal films, according to, for example, the travel-through principle which is characterized by the fact that sensitizing is achieved by means of acid solutions of compounds of trivalent elements of the 5th Main Group of the Periodic Table (Mendelyeev), preferably of trivalent arsenic, antimony, or a combination thereof.

Preferred are aqueous solutions, combined with hydrochloric acid, sulfuric acid, or nitric acid, of the salts, e.g. halides, sulfates, nitrates, oxychlorides, oxynitrates, carbonates, or oxides, of arsenic or antimony, especially of the arsenic (III) oxide or AsCl in hydrochloric acid solution. In general, the Group III compound can be one which is soluble in and ionizes in aqueous acid, e.g. inorganic acid, solution. The solution can have a pH of 0.3-2.5, preferably 0.5-1.5.

The sensitizing is performed preferably in the presence of hydrolyzable tin (IV) compounds acting as wetting agents, especially SnCl and in the presence of soluble halides or nitrates of ammonium and/ or the alkali metals (lithium, sodium, or potassium) and/or alkali earth metals (especially calcium and herein including magnesium) which acts as stabilizers.

An effect of sensitizing in accordance with the invention is that it makes possible the use, as a pickling bath, of diluted acids, e.g. diluted chromosulfuric acid (5-10 g. CrO /l. liter 50-60% by Weight sulfuric acid), and a pickling reaction temperature of 50-70" C.

Moreover, the process makes it possible to perform the reductive sensitizing phase-as in the case of conventional processes-prior to the activation phase.

As activation baths, one may use a dilute, aqueous, strongly acid palladium salt solution, especially dilute hydrochloric or sulfuric acid, PdCl solution or PdSO solution in the pH range between 1 and 3, for instance of a strength of 0.2-5 g. PdCl in 5-20 ml. concentrated HCl/liter.

THE PROCESS In accordance with the invention, the reaction steps can be performed in the following sequence:

(a) Pickling in, e.g. chromosulphuric acid to precondition the surface.

(b) Sensitizing with acid, aqueous solutions of trivalent antimony or arsenic compounds, especially arsenic, which may contain in addition hydrolyzable tin (IV) compounds as well as alkali, alkaline earth, and/or ammonium halides and/or nitrates, especially ammonium chloride.

(0) Activating the surface for chemically plating thereon of a first metal coating, in, e.g. dilute noble metal, e.g. palladium salt, solution, especially in hydrochloric or sulfuric acid palladium chloride solution.

(d) Chemical depositing of said first metallic conductor layer comprising for instance, nickel and/or copper from nickel or copper baths to prime the surface for electrolytically plating thereon of a second metal coat- (e) Electrolytically or galvanic reinforcement by means of a plating metal such as nickel, copper, chromium, silver, gold or several of these metals, which .forms said second metal coating. Surprisingly, metallizing of the auxiliary or support electrodes does not occur.

Throughout the entire process, the items to be metallized can remain on the supports designed as electrodes. After each passage through the process, the support electrodes can be dipped briefly into an oxidizing acid, for instance chromosulfuric acid, nitric acid etc. and can then be used again. The support electrode can be isolated by a coating resistant to chromosulfuric acid, e.g. a coating of polyvinyl chloride.

THE PLASTICS The invention is generally applicable to the known metallizable plastics.

This process is particularly valuable in the metallizing of metallizable polyvinyl types and in metallizing processes in which one conductor layer is to be deposited by reduction from nickel salt solutions while the support electrodes remain free of metal.

As metallizable polyvinyl types there can be used for instance the copolymers of vinyl chloride with 420% by Weight fumaric acid diesters, and/r maleic acid diesters wherein at least one of the alcohol moieties of the diester is a C -C or C to C group or copolymers of the vinyl chloride with polymerizable comonomers containing long chain alkyl groups (e.g. 8-30, preferably 14-26 carbon atoms), such as vinyl ester of preferably long chain carboxylic acids of the general formula CH CHOOCR, viny-l ether of the formula CH CHO-R wherein R is C -C or C -C or esters and diesters of itaconic acid, fumaric acid, acrylic acid, methacrylic acid, wherein there is at least one long chain alkyl group, as defined above, or allyl ester preferably of long chain oarboxylic acids e.g. C -C or C14-C25, especially monocarboxylic acids, e.g. stearic acid. Of the alkyl groups referred to, any can be employed, e.g. the straight chain C C ,C 'C etc. to C Others suitable plastics are chlorinated polyethylene, mixtures of chlorinated polyethylene and polyvinyl chloride, mixtures of polyethylene and chlorinated polyvinyl chlorides, copolymers of vinyl chloride with ethylene as well as graft polymers of vinyl chloride on vinyl chloride copolymers, and also polyolefins, such as polypropylene or poly-4-methyl-pentene-(1), polyester, etc.

As indicated, the invention is not limited to the plastics particularly referred to but, generally speaking is applicable to metallizable plastics, including such as ABS polymers, i.e. copolymers and graft polymers of the acrylonitrile, butadiene and styrene, containing as a rule 10-30% by weight acrylonitrile, 50-70% by Weight styrene and 8-25 by weight butadiene, metallizable polypropylene types consisting for instance of isotactic polypropylene containing relatively large amounts of an ionogenic, conductive filler material such as zinc sulfide, titanium dioxide, barium sulfate, etc., polysufones, polyacetals, polyesters, polyamides, and others, as well as mixtures of the plastics mentioned.

Mixtures of the said ABS types and polypropylene types with PVC, post-chlorinated PVC, chlorinated polyethylene, chlorinated polypropylene and others are metallizable in this manner.

Metallizable PVC types have been described in the Belgium Pats. 713,290 and 718,487. Those materials can be used in the instant process.

Polyvinylchloride, modified polyvinyl chloride, or other plastics resistant to chromosulfuric acid can be ,used as electrode insulating material. In his way coating of the electrode with metal during a travel-through process can be prevented.

THE SENSITIZING SOLUTION Another object of the invention is a sensitizing solution for the sensitizing of plastics to be metallized and consisting of acid solutions of compounds of the trivalent arsenic or antimony.

This sensitizing solution can contain 0.5-40 g./ liter, preferably 1-10 g./liter of compounds of the trivalent arsenic, computed on a chemically equivalency basis as PRODUCTS The metallized plastics manufactured by means of this sensitizing solution exhibit a perfectly smooth surface and a good adhesion of the metal coating onto the plastic surface.

Percentages denote percent by weight, unless otherwise indicated.

Preparation of sensitizing solutions suitable for the travel-through process is described in Examples 1-3.

Example 1 (a) 2.5 arsenic (III) oxide are dissolved in 20 cc. conc.

HCl.

(b) 30 g. SnCL; are hydrolyzed in 200 cc. Water.

(c) 60 g. NH Cl are dissolved in 200 cc. water.

These are mixed in the sequence (b)+(c) (a) and filled with water to 1 liter.

Example 2 (a) 4 g. arsenic (III) oxide are dissolved in 30 cc. conc.

HCl

(b) 15 g. SnCL, are hydrolyzed in 200 cc. water. (c) g. ammonium nitrate are dissolved in 200 cc.

water.

(a), (b), and (c) are added in the squence and filled with water to a volume of 1 liter.

Example 3 (a) 15 g. arsenic (III) oxide are dissolved in 50 cc. conc.

HCl.

(b) 15 g. SnCl are hydrolyzed in 200 cc. water.

(0) 60 g. ammonium chloride and 60 g. CaCl are dissolved in 200 cc. water.

Following mixing in the sequence (b)+(c);+ (a), the solution is filled with water to 1 liter.

One obtains clear, colorless solutions that remain for weeks free from any deposits.

Metallizing of plastics as per the travel-through process according to the invention is described in Examples 4-7.

One obtains clear, colorless solutions that remain for weeks free from any deposits.

Metallizing of plastics as per the travel-through process according to the invention is described in Examples 4-7.

Example 4 As metallizable polyvinyl chloride types one can use the following copolymers of the vinyl chloride:

(a) 92 percent by weight VC, 8% by weight fumaric acid dicetyl ester or 8% by weight maleic acid dicetyl ester.

(b) 89 percent by weight VC, 11% by weight maleic acid distearyl ester.

(c) 92 percent by weight VC, 8% by weight acrylic acid stearyl ester.

(d) 86 percent by weight VC, 14% by weight lauryl vinyl ether.

(e) 96 percent by weight VC, 4% by weight ethylene (CI content 50.8% by wt.).

A pressed sheet made of any one of the said materials and having the dimensions 4.0 x 9.0 x 0.4 is treated by the travel-through process as follows:

(1) is pickled in chromosulfuric acid (8 g. CrO dissolved in 1 liter 60% sulfuric acid) for 10 minutes at 60 C.;

(2) following rinsing with water, the plate is dipped into an arsenic containing sensitizing bath (prepared discretionally according to Examples 1, 2 or 3) for 2-5 minutes at 25 C.;

(3) following another rinsing with water, the plate is dipped into hydrochloric acid or sulfuric acid containing palladium salt solution for a period of 2-5 minutes (e.g. 0.1 to 0.25 PdCl dissolved in 10 cc. conc. HCl and filled with water to 4 liters) at 25 C.;

(4) following another rinsing, the plate is dipped into a chemical nickel bath containing 30 g./l. NiSO -7H O and 30 g./l. NaH PO -H O at 60 C. Within 3 minutes it becomes completely coated with metallic nickel; the support electrode remains free from metal;

(5) the galvanic reinforcing of the metal coating can then be, alternatively, a per se known dull finish plating, high luster copper depositing, high luster nickel depositing or chromium plating. :In this example, the sheet is plated with high luster copper plating by a solution containing 255 g./l. CuS -H O; 120 g./l. H 80 conc. and 8 g./l. HCl.

The adhesive strength of the metal coating applied in this manner onto the plastic amounts, according to DIN 40,802, to between 6 and 8 kp.

Following removal of the galvanized item, the support electrode is dipped briefly into chromosulfuric acid or nitric acid and can then be reused.

Example 5 In the travel-through process, as ABS graft polymers one uses the following polymers of the composition (a) 25% by weight acrylonitrile, 10% by weight butadiene and 65% by weight styrene.

(b) 24% by weight acrylonitrile, 16% by weight butadiene and 60% by weight styrene.

(c) 21% by weight acrylonitrile, by weight butadiene and 64% by weight styrene.

and performs the treatment as follows at the temperatures employed in Example 4:

A pressed plate of the size 4.0 x 9.0 x 0.4:

( 1) is pickled in chromosulfuric acid (8 g. CrO dissolved in 1 liter of 60% sulfuric acid) for 12 minutes;

(2) following rinsing with water, the plate is dipped into an arsenic containing sensitizing bath, according to Examples 1, 2 or 3, for 2-5 minutes;

(3) following another rinsing with water, the plate is dipped for 2-5 minutes into a palladium salt solution containing hydrochloric acid or a corresponding amount of sulfuric acid (e.g. 0.1-0.25 g. PdCl dissolved in 10 cc. conc. HCl and filled with water to 4 liter);

(4) after another rinsing, the plate is dipped into a chemical nickel bath. Within three minutes, the surface is completely coated with metallic nickel. The electrodes remain free from metal;

(5) further processing is conducted as in Example 4.

The adhesive strength of the metal coating applied in this manner is, according to DIN 40,802, 7.0 hp. The electrode is treated as in Example 4.

Example 6 Pressed plates measuring 4.0 x 9.0 x04 made of ABS graft polymers of the following composition:

(a) 25% by wt. acrylonitrile, 21% by wt. butadiene, and

54% by wt. styrene.

(b) 25% by wt. acrylonitrile, 14% by wt. butadiene, and

61% by wt. styrene.

6 (c) 27% by wt. acrylonitrile, 22% by wt. butadiene, and

51% by wt. styrene.

at temperatures employed in Example 1, are treated by the travel-through process. They are pickled in chromosulfuric acid (300 g. CrO dissolved in one liter of 20% sulfuric acid) for 10 minutes. Following rinsing with water, the plates are dipped for 2-5 minutes into the arsenic-containing sensitizing bath (Examples 1-3). Following further rinsing with water, the plate is dipped into a dilute palladium salt solution containing hydrochloric or sulfuric acid (c.g. 0.25 g. to 5 g. PdCl dissolved in 10 cc. conc. HCl and filled with water to 4 liters) for 2-5 minutes. Following further rinsing, the plate is dipped into a chemical copper bath. Within 3 minutes, the plate is coated with a metallic copper layer. The electrodes remain free from metal. The further galvanic treatment proceeds as described in Example 4. The adhesive strength of the metal film deposited onto the plastic surface amounts, according to DIN 40,802, to 6.3 kp.

For the treatment of the electrodes see Example 4.

Example 7 As a metallizable polypropylene there is used an isotactic polypropylene having a filler content of 28.1% ZnS, 0.4% BaSO, and 1.4% ZnO, and treated in the travel-through process as follows.

A pressed plate measuring 4.0 x 9.0 x 0.4, at tempera tures employed in Example 1, is pickled for 10 minutes in chromosulfuric acid (54.5 g. CrO dissolved in 1 liter of a 92% sulfuric acid solution). Following rinsing with water, the plate is dipped for 3-5 minutes into the arsenic containing sensitizing bath (Example 1-3). Following further rinsing with water, the plate is dipped into an acid palladium salt solution for 2-5 minutes (2.5 g. PdCl dissolved in 10 cc. conc. HCl and filled with water to 4 liters). Following another rinsing, the plate is dipped into a chemical nickel bath. Within three minutes it becomes completely coated with metallic nickel. The support electrodes remain free from metal. The further galvanic treatment occurs in accordance with Example 4. The adhesive strength of the metal film applied in this manner amounts, according to DIN 40,802, to 7.5 kp. Treatment of the electrodes is as in Example 4.

In the same way it is also possible to metallize an isotactic polypropylene containing 1% titanium dioxide.

In the examples antimony can be used in place of arsenic.

Other metals which can be used in place of arsenic and antimony are bismuth, preferably in combination with arsenic.

By concentrated HCl is meant such of 38 weight percent HCl content in aqueous solution.

What is claimed is:

1. In a process of metallizing a metallizable plastic article comprising:

(a) pickling the article to precondition the surface,

(b) sensitizing the surface for the metallizing thereof,

(c) activating the surface for chemically plating thereon a first metal coating,

(d) chemically plating said first metal coating thereon to prime the surface for electrolytically plating thereon a second metal coating, and

(e) electrolytically or gal-vanically plating said second metal coating thereon,

the improvement which comprises:

sensitizing is step (b) by contacting the pickled surface with an aqueous acid solution of: (1) a compound of trivalent arsenic or antimony or a mixture thereof, and (2) at least one quadrivalent hydrolyzable tin compound.

2. Process according to claim 1, the pH of the sensitizing solution being 0.5-2.5.

3. Process according to claim 1, wherein said trivalent metal is arsenic.

4. Process according to claim 1, wherein said activating of the surface comprises contacting the surface with an acid solution of palladium chloride.

5. Process according to claim 1, wherein said plastic is a polyvinyl chloride polymer.

6. Process according to claim 1, wherein said first metal coating is nickel.

7. Process according to claim 1, wherein said tin compound is SnCl 8. Process according to claim 7, said sensitizing solution containing a soluble halide or nitrate of an alkali metal, alkali earth metal or ammonium or a mixture thereof.

9. Process according to claim 7, said sensitizing solution containing ammonium chloride.

10. Process according to claim 1, the sensitizing solution consisting essentially of:

(a) 0.5 to 40 g./liter of said trivalent arsenic or antimony compound or mixture thereof, computed on a chemically equivalency basis of A5 0,; and

(b) 2 to 200 g./liter of said quadrivalent tin compound, calculated as SnCl 11. Process according to claim 10, the sensitizing solution containing:

-300 g./liter of halide or nitrate of an alkali metal, alkali earth metal or ammonia or a mixture thereof.

12. Process according to claim 10, the sensitizing solution containing at least one of hydrochloric, sulfuric, and nitric acid; 1 to 10 g./1iter trivalent arsenic compound calculated as As O 4 to g./liter of SnCl -150 g./liter of NH Cl or NH NO or a mixture thereof.

References Cited UNITED STATES PATENTS 3,620,834 11/1971 Duffy 117-47 A 3,379,556 4/1968 Chiecchi 117-47 A 2,551,342 5/ 1951 Scholl 204-30 2,551,344 5/1951 Scholl 204-30 3,484,270 12/ 1969 Saubestre et al. 117-47 A 3,547,784 12/ 1970 Bernhardt 204-20 3,556,956 1/1971 Miller 204-30 2,586,477 2/1952 Niles 117-161 W 3,510,327 5/1970 Miller 117-47 A 3,408,211 10/1968 Coates 117-160 R 2,834,724 5/ 1958 Mendes 204-30 WILLIAM D. MARTIN, Primary Examiner W. R. TRENOR, Assistant Examiner U.S. C1. X-R.

117-47 A, 118, E, R, 213, 227; 204-20, 30 

